Crystallization in Partially Amorphous Ni<SUB>50</SUB>Ti<SUB>32</SUB>Hf<SUB>18</SUB> Melt Spun Ribbon

Abstract

A partially amorphous Ni 50 Ti 32 Hf 18 melt spun ribbon has been characterized by means of calorimetry, X-ray diffraction and transmission electron microscopy, showing that the amorphous regions are mostly concentrated in the wheel side as a consequence of a higher cooling rate during the fast solidification (i.e. higher solidification rate). Special emphasis has been given to the crystallization process of the amorphous regions, studying the evolution of the microstructure and the martensitic transformation. Although several crystallization procedures have been carried out by thermal treatments, either slightly under or over the crystallization temperature measured by DSC, T C , the final microstructure and calorimetric behavior of the fully crystalline samples does not depend on the applied temperature. The fully crystalline samples contain regions with small crystallites produced during the thermal treatment (showing that the crystal nucleation energy is rather low for this alloy) together with the large crystals originated during the melt-spinning. At room temperature (RT), both types of crystals are in martensitic state. The new crystallized regions with small grain size show notably lower transformation temperatures and higher hysteresis in comparison to the big crystals already existing before the crystallization treatments. However, an additional mechanism, apart from the crystal size, affects the transformation temperatures, likely related to the presence of more defects (mainly grain boundaries) in the crystallites created by thermal treatments. These defects could act as nucleation sites for the martensite and increase the transformation temperatures with respect to the as cast spherical crystallites of similar sizes.

Glass forming ability: Miedema approach to (Zr, Ti, Hf)–(Cu, Ni) binary and ternary alloys

“…Similarly, in the Zr-Ti-Ni and Zr-Hf-Ni system glass formation has been reported at Zr rich, Hf rich and Ni rich compositions [38,39,[41][42][43][44]. In the Hf-Ti-Ni system the only known report shows the formation of partially amorphous structure at one composition [40]. These compositions also lie within the predicted composition range.…”

Crystallization of the amorphous phase and martensitic transformations in multicomponent (Ti,Hf,Zr)(Ni,Cu)-based alloys

“…composition produced by melt-spinning and interesting due to their shape memory properties, were the subject of numerous investigations of the crystallization processes, the resulting microstructure and martensitic transformations [13][14][15][16][17]. Melt-spun TiNi-based ribbons with additions of Cu, Zr, Hf and other elements were also studied [18][19][20][21]. The present paper describes research in the thermophysical properties of some rapidly solidified multicomponent (Ti,Zr,Hf,Nb) A (Ni,Cu,Co,Pd,Ag,Al) B alloys, as well as the effect of a crystallization thermal treatment on the characteristics of martensitic transformations.…”

Structure of multi-grain spherical particles in an amorphous Ti50Ni25Cu25 melt-spun ribbon

“…However, in theory, it might be possible to control the final crystalline structure, and thus some properties of the martensitic transformation, only modifying the crystallization parameters. Several works based on this new attractive idea have been carried out in Ni-Ti-based alloys (Ti 50 Ni 25 Cu 25 [4,5] and Ni 50 Ti 32 Hf 18 [6]). …”